gfan_tropicalhypersurface: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/gfan_tropicalhypersurface - from package: gfan

You may install the required package with command apt-get install {package}
Error in other languages:
gfan_tropicalhypersurface: bevel nie gevind nie
gfan_tropicalhypersurface: comandă negăsită
gfan_tropicalhypersurface: comando não encontrado
gfan_tropicalhypersurface: commande introuvable
gfan_tropicalhypersurface: command not found
gfan_tropicalhypersurface: käsku ei ole
gfan_tropicalhypersurface: không tìm thấy lệnh
gfan_tropicalhypersurface: komanda nerasta
gfan_tropicalhypersurface: Kommando nicht gefunden.
gfan_tropicalhypersurface: kommandot finns inte
gfan_tropicalhypersurface: komut yok
gfan_tropicalhypersurface: nie znaleziono polecenia
gfan_tropicalhypersurface: níor aimsíodh an t-ordú
gfan_tropicalhypersurface: no se encontró la orden
gfan_tropicalhypersurface: no s'ha trobat l'ordre
gfan_tropicalhypersurface: opdracht niet gevonden
gfan_tropicalhypersurface: parancs nem található
gfan_tropicalhypersurface: perintah tidak ditemukan
gfan_tropicalhypersurface: príkaz nenájdený
gfan_tropicalhypersurface: příkaz nenalezen
gfan_tropicalhypersurface: команда не найдена
gfan_tropicalhypersurface: командата не е открита
gfan_tropicalhypersurface: 命令找不到
gfan_tropicalhypersurface: コマンドが見つかりません